1. Field of the Invention
The present invention relates to a fixing device for fixing a toner image onto a transfer member, and an image forming apparatus provided with the same.
2. Description of the Related Art
Image forming apparatuses such as a copying machine, a printer, and a facsimile machine include an image forming section for forming a visible toner image from an electrostatic latent image formed on a photoconductive member and transferring the toner image onto a transfer sheet, and a fixing device for fixing the toner image onto the transfer sheet.
As shown in FIG. 5, the fixing device includes a known belt-type fixing device in which an endless fixing belt 100 is wound around a fixing roller 101 and a support roller 102. In this fixing device, the fixing roller 101 is pressed by a pressing roller 103 in such a state where the fixing belt 100 is nipped between the fixing roller 101 and the pressing roller 103 (for example, refer to Japanese Patent Unexamined Publication No. 2004-77871).
Meanwhile, a color image forming apparatus uses greater amount of toners at a time of fixing than a monochromatic image forming apparatus does. Therefore, it is necessary to have a longer time (nipping time) of allowing a transfer sheet to be in contact with the fixing belt. Accordingly, as shown in FIG. 5, a slide pressing member 110 is arranged on an upstream side of the fixing roller 101 and on an inner side of the fixing belt 100. The slide pressing member 110 presses the pressing roller 103 while the fixing belt 100 being sandwiched between the fixing roller 101 and the pressing roller 103.
As shown in FIG. 6, the slide pressing member 110 is supported by a pivot shaft 110a parallel to a rotational shaft 103a of the pressing roller 103. Therefore, the pressing roller 103 can be pressed evenly in a circumferential direction of the pressing roller 103.
However, a state of pressure applied by the slide pressing member 110 along a longitudinal direction (rotation axis direction) of the pressing roller 103 depends on parts accuracy of the slide pressing member 110, the pressing roller 103, and the like. Thus, for example, in a case where a change in an outer diameter of the pressing roller 103 occurs, a tension between the slide pressing member 110 and the pressing roller 103 differs along a longitudinal direction of the pressing roller 103. As a result, running of the fixing belt 100 is disturbed on a side having a greater tension so that disadvantageous snaking of the fixing belt 100 occurs. Further, unevenness in the tension along the longitudinal direction of the pressing roller 103 had been likely to cause unevenness in luster.